1. Field of the Invention
The present invention relates to an optometric apparatus including an eye refractive measuring apparatus and a cornea shape measuring apparatus and others.
2. Description of Related Art
Generally, an eye refractive measurement apparatus and a cornea shape measuring apparatus are for measuring a direction of axis of an eye to be examined, such as astigmatic axis and principal meridian, and therefore need precise alignment between an eye to be examined and the apparatus unit. If the alignment between an eye to be examined and the apparatus unit is not precise, it will be inavoidable that the measured data obtained with such apparatus have errors therein.
In a conventional eye refractive measurement apparatus and the like, to effect alignment with an eye to be examined, utilized is a method of fixedly supporting the head of the examinee on a head or forehead support member so as to correspond with a direction of a reference axis of a measuring system.
The recent optometric apparatus utilizes a monitor to project image of the anterior part of the eye to be examined, accordingly, the alignment situation can be partially found based on the monitored image. For instance, U.S. Pat. No. 4,755,041 discloses such measuring apparatus.
There is also known an eye refractive power measuring apparatus with a system for measuring interpupilary distance which is a distance between each visual axes of a right and a left eyes of an examinee. For instance, U.S. Pat. No. 5,152,067 discloses such eye refractive power measurement apparatus in which the interpupilary distance is detected by measuring the moving distance of the measuring optical system from an alignment position with respect to an eye to another alignment position with another eye.
In apparatuses mentioned above, although at least the examinee's head is fixed on the head support member, there is no assurance that the right and left eyes of the examinee are certainly in a horizontal and, if anything, strictly, these eyes are commonly inclined off the horizontal. And further, according to differences among individuals, there are quite a few instances that the inclination of the eyes is remarkable. It is, therefore, difficult to obtain accurate data about astigmatic axis and principal meridian by the conventional apparatuses.
In the apparatus shown in U.S. Pat. No. 4,755,041, the anterior part of an eye is to be observed on a monitor, but it is just only a part around the pupil of the eye and therefore the examiner can find that both eyes are not in a horizontal only if an eye is extremely inclined.
And also, in the measurement of interpupilary distance taught in U.S. Pat. No. 5,152,067, when both eyes of the examinee are not in a horizontal, results obtained must include errors.